    Patent document 1: JP-A-2007-220323
Dissolution and elution of a catalyst component (e.g. Pt, Rh, Pd, or the like) in an electrode catalyst in a fuel cell have been studied conventionally. Many research findings reported about a mechanism of the dissolution and the elution. According to a certain report, since a platinum oxide dissolves in a solution, it is supposed that platinum may dissolve via the platinum oxide. As an electric potential in the solution becomes high, the amount of the elution of platinum may become large, and the platinum oxide formation may be promoted. When cell voltage (corresponding to an electric potential in a fuel cell) becomes high, platinum or the like in an electrode catalyst layer in the catalyst component may be easily eluted. The elution of platinum or the like may cause degradation and a performance deterioration of the fuel cell.
Electrical voltage generated by a fuel cell changes according to an output of the fuel cell. When the output of the fuel cell becomes high, the voltage of the fuel cell will decrease. When the output of the fuel cell becomes low, the voltage of the fuel cell will increase. In this case, accompanying with a change of voltage, platinum or the like in, especially, a cathode catalytic layer of an oxidant electrode may be eluted, and a performance deterioration of the fuel cell may be caused.
For example, in patent document 1, in order to prevent degradation and a performance deterioration of the fuel cell, when a state of charge (SOC) of a secondary battery is higher than 10%, an output control portion restricts the output of the fuel cell. In addition, the voltage of the fuel cell may not be lower than a predetermined voltage. Accordingly, an electrical potential of the oxidant electrode in the fuel cell is kept high, a variation of the electrical potential of the oxidant electrode is kept low. An oxide layer in a platinum surface of the cathode catalytic layer of the oxidant electrode may not be reduced and may not elute. In addition, it may be possible to prevent the platinum from eluting when a brake pedal of a vehicle is stepped on, the output of the fuel cell becomes low, and the electrical voltage of the fuel cell becomes high.
The inventor of the present invention has found the following with respect to a fuel cell. In patent document 1, when a state of charge of the secondary battery is high, it is required that an auxiliary machine consumes a generated power of the fuel cell or the output of the fuel cell should be reduced. However, in this case, deterioration of fuel efficiency, degradation or a performance deterioration of the fuel cell may occur.